Method of marking sintered body and method for manufacturing magnetic head wafer

ABSTRACT

A method of marking a sintered body includes the step of preparing the sintered body by sintering a mixture of first and second types of powder particles. The first type of powder particles is made of a first material and the second type of powder particles is made of a second material that has a different etch susceptibility from the first material. The method further includes the step of writing ID information on the surface of the sintered body by forming a first concave region to a depth of at least about 10 nm under the surface of the sintered body and a second concave region under the first concave region, respectively. The first concave region is formed by etching away both the first and second types of powder particles, while the second concave region is formed by etching away only the first type of powder particles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of marking a sintered bodywith ID information and more particularly, relates to a method ofmarking a sintered body with ID information having high contrast whileminimizing contamination. The present invention also relates to a methodfor manufacturing a wafer for magnetic heads including performing amarking process and further relates to a sintered body that has beenmarked with ID information, a magnetic head, and a storage medium drive.

2. Description of the Related Art

Recently, a thin-film magnetic head having any of various structuresoften includes a magnetic head slider for use in a hard disk drive(HDD), a tape storage and a flexible (or floppy) disk drive (FDD), forexample. Examples of wafers for such a thin-film magnetic head includesintered wafers having compositions such as Al₂O₃—TiC, SiC and ZrO₂.

FIG. 1A illustrates a typical thin-film magnetic head slider 10. On itstracking side, this magnetic head slider 10 includes two side rails 11that are arranged to be opposed to the surface of a magnetic disk. Thesurface of the thin-film magnetic head slider 10 on which the side rails11 are provided is sometimes called an “air bearing surface (ABS)”. Ifthe magnetic disk is rotated at a high velocity by a motor, for example,while the surface of the magnetic disk is pressed lightly by the siderails 11 of the magnetic head slider 10 by way of a head suspension,then an air layer will be formed on the surface of the magnetic disk andwill reach the back surface of the air bearing surface of the slider 10.As a result, the magnetic head slider 10 is slightly lifted up. In thismanner, the magnetic head slider 10 can perform read and writeoperations on the magnetic disk while “flying” near the surface of thedisk so to speak.

A thin film 12, which causes a magnetic interaction with a storagemedium such as a magnetic disk, is deposited on one end surface of themagnetic head slider 10. The thin film 12 is used to form part of anelectrical/magnetic transducer. To indicate the type of the product, anidentifier (ID or ID mark) 13 such as a serial number is inscribed onthe other end surface of the magnetic head slider 10. Methods ofinscribing an identifier 13 on sintered wafers are disclosed in JapaneseLaid-Open Publications Nos. 9-81922, 10-134317 and 11-126311, forexample.

In a typical manufacturing process, the magnetic head slider 10 isobtained by cutting out a bar 20 shown in FIG. 1B from a sintered wafer1 shown in FIG. 1C and then dicing the bar 20 into a great number ofchips. In FIG. 1C, the end surface 4 of the sintered wafer 1 is parallelto the air bearing surface of the magnetic head slider 10 shown in FIG.1A.

Recently, as the sizes of such a thin-film magnetic head have beendecreased to reduce the sizes and weight of an electronic appliance, thethickness of the sintered wafer 1 (corresponding to the length L of themagnetic head slider 10) and the thickness T of each bar 20(corresponding to the height of the magnetic head slider 10) have alsobeen reduced. For example, a magnetic head slider, which is called a“pico-slider”, has a length L of about 1.2 mm and a thickness T of about0.3 mm. As for a magnetic head slider of such drastically reduced sizes,the sizes of characters to be inscribed on the slider should also bereduced correspondingly.

In the prior art, a laser marking method is often used to inscribe theidentifier 13 (this process step will be sometimes referred to herein asa “marking” process step or an “ID marking” process step). In the lasermarking method, the identifiers 13 shown in FIGS. 1A and 1B are markedon the back surface 3 of the wafer 1 that is yet to be divided into thebars 20. After the marking process step is finished, various thin films12 are stacked on the front surface 2 of the wafer 1.

Hereinafter, the conventional laser marking method will be describedbriefly with reference to FIG. 2.

In the laser marking method, the back surface 3 of the sintered wafer 1is locally irradiated with a laser beam 6 that has been converged by alens 5, thereby rapidly heating and vaporizing the irradiated portion ofthe wafer 1. In this case, a tiny concave portion is formed on the backsurface 3 of the wafer 1, while the material of the sintered wafer 1 isscattered around and just a portion of the scattered material isdeposited on the wafer 1 again. By scanning the back surface 3 of thewafer 1 with the laser beam 6, the concave portions can be arranged soas to form an arbitrary pattern on the back surface 3 (which will bereferred to herein as a “concave pattern”). Any of various types ofidentifiers 13 can be written at an arbitrary location on the wafer 1 byforming a concave pattern, which is made up of alphanumeric and/ornumeric characters or a barcode, on the back surface 3 of the wafer 1.

A laser marking method as described above, however, has the followingdrawbacks.

Firstly, the portion of the sintered material that has been scatteredaround as a result of the exposure to the laser beam is likely adsorbedor deposited as dust onto the inscribed characters, thus causing acontamination problem in many cases.

Secondly, the edges of the inscribed characters are often burred throughthe exposure to the laser beam. Thus, a deburring processing step needsto be carried out.

FIG. 3 schematically illustrates a cross section of a sintered wafer 1on which characters have been marked by the conventional laser markingmethod. This cross-sectional view is drawn after a scanning electronmicroscope (SEM) photograph has actually been taken. As shown in FIG. 3,a deep concave portion 30 is formed on the surface of the wafer 1 as aresult of the laser beam exposure. As measured from the back surface ofthe wafer 1 in the direction indicated by the arrow a in FIG. 3, theconcave portion 30 has a depth of about 30 μm to about 50 μm. A convexportion (or burr) 31 is also formed around the edge of the concaveportion. As also measured from the back surface of the wafer 1 in thedirection indicated by the arrow b, the burr 31 has a height of severalμm. The concave portion may have a width of about 20 μm, for example.

As shown in FIG. 3, a huge number of particles 32 are deposited on theinner surface of the deep concave portion 30 that has been formed as aresult of the laser beam exposure. Strictly speaking, some of thoseparticles 32 may have such irregular shapes that cannot be classifiedamong “particles”. However, those irregular ones will also be referredto herein as “particles” for the sake of simplicity. To remove thoseparticles 32 from the wafer 1, a cleaning process such as an ultrasoniccleaning process must be carried out for a long time after the markingprocess is finished. Even so, it has still been difficult to remove mostof the particles 32 that have reached the depth of the concave portion30.

If a huge number of particles 32 are created during the marking process,some of those particles may be dispersed in the cleaning liquid and thendeposited on the other side (i.e., the front surface 2) of the wafer 1that has not been exposed to the laser beam. In that case, when aninsulating thin film of amorphous aluminum oxide, for example, isdeposited on the front surface 2 of the wafer 1 with the re-depositedparticles 32, then those particles 32 might be introduced into theinsulating film. Also, the surface of such an insulating thin film isnormally planarized before a magnetic thin film is deposited thereon.Accordingly, if the insulating thin film includes the particles 32,portions of the insulating thin film may peel off locally along with theparticles 32 to possibly create pinholes in the insulating thin filmduring the planarizing process. Also, even if no such pinholes have beencreated, a portion of the insulating thin film may have its thicknessdecreased significantly by the particles 32. Then, that portion of theinsulating thin film may exhibit decreased insulating properties.Furthermore, even when no such particles enter the insulating film, themarked portion of the back surface of the wafer 1 may still be a dustsource. Then, the yield may decrease in a number of subsequentmanufacturing process steps, and the quality of the final product itselfmay deteriorate.

Accordingly, to increase the production yield of thin-film magneticheads, the insulating film to be deposited on the sintered wafer 1preferably is as high quality as possible. For that purpose, theconditions for the marking process are preferably controlled so as toeliminate the dust or contamination problem. In addition, once completedas a product, the magnetic head needs to be used in a clean environment.Thus, the presence of any dust would also be a problem that affectsnormal operation of the magnetic head.

Meanwhile, methods of writing ID information on a sintered wafer by achemical etching process have also been proposed as replacements for thelaser marking process. For example, the applicant of the presentapplication disclosed a technique of forming a shallow concave portionby a chemical etching process while increasing the contrast in JapaneseLaid-Open Publication No. 2001-334753. According to this technique, acompound sintered body, made of at least two types of powder particleswith mutually different etch susceptibilities, is subjected to aselective etching process such that one of the two types of powderparticles is etched preferentially. As a result of such a selectiveetching process, an unevenness of a very small size, corresponding tothe size of the powder particles, is formed on the surface of thecompound sintered wafer. Such an unevenness decreases the reflectivityof the wafer surface, thereby creating a difference in contrast betweenthe etched and non-etched portions of the wafer.

The selective etching process disclosed in Japanese Laid-OpenPublication No. 2001-334753 can resolve the dust or contaminationproblem. However, according to this technique, the contrast of thereflected light is not high enough to increase the recognition rate ofthe ID information sufficiently.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a method of marking a sintered body byan etching process with the recognition rate of ID information beingsignificantly increased, and also provide methods of making qualitysintered bodies, magnetic head wafers, magnetic heads and storage mediumdrives with very high yields by performing the marking process step ofthe marking method of the present invention.

According to a preferred embodiment of the present invention, a methodof marking a sintered body includes the step of preparing a sinteredbody by sintering a mixture of a first type of powder particles and asecond type of powder particles. In this case, when the first type ofpowder particles is made of a first material, the second type of powderparticles is preferably made of a second material that has a differentetch susceptibility from the first material. The method preferablyfurther includes the step of writing ID information on the surface ofthe sintered body by defining a first concave region to a depth of atleast about 10 nm under the surface of the sintered body and a secondconcave region under the first concave region, respectively. In thisprocess step, the first concave region is preferably defined by etchingaway both the first and second types of powder particles, while thesecond concave region is preferably defined by selectively etching awayonly the first type of powder particles.

In one preferred embodiment of the present invention, the step ofwriting the ID information preferably includes the step of defining thesecond concave region to a depth of at least about 50 nm under thebottom of the first concave region.

In another preferred embodiment, the step of writing the ID informationpreferably includes the steps of performing a selective etching processsuch that the first type of powder particles are etched at a higher ratethan the second type of powder particles, and performing a non-selectiveetching process such that the first and second types of powder particlesare etched at substantially equal rates after the selective etchingprocess has been carried out.

In this particular preferred embodiment, the step of writing the IDinformation preferably includes the step of performing the selectiveetching process and/or the non-selective etching process multiple times.

Specifically, the step of writing the ID information preferably includesthe step of performing the non-selective etching process at least as thelast etching process thereof.

In another preferred embodiment, the selective etching process and thenon-selective etching process are preferably carried out by the sameetching system with etching conditions being changed.

In still another preferred embodiment, the first and second types ofpowder particles may both have a mean particle size of about 0.3 μm toabout 5.0 μm.

In yet another preferred embodiment, the first concave region preferablyhas a line width of about 1 μm to about 20 μm.

In yet another preferred embodiment, a variation ΔR in reflectance dueto the selective etching process is preferably at least about 25% withrespect to light having a particular wavelength. The variation ΔR isdetermined by (R2−R1)/R2, where R1 is the reflectance of a portion ofthe surface of the sintered body that has been subjected to theselective etching process and R2 is the reflectance of another portionof the surface of the sintered body that has not been subjected to theselective etching process.

In this particular preferred embodiment, the particular wavelength ispreferably included in the wavelength range of light to be radiatedtoward the sintered body to read the ID information optically.

In yet another preferred embodiment, a portion of the surface of thesintered body, which has not been subjected to the selective etchingprocess, preferably has a surface roughness of at most about 5 nm.

In yet another preferred embodiment, the depth of the second concaveregion is preferably about 50 nm to about 5 μm as measured from thebottom of the first concave region.

In yet another preferred embodiment, the first and second materials arepreferably compounds selected from the group consisting of aluminumoxide, aluminum nitride, silicon oxide, silicon nitride, zirconiumoxide, zirconium nitride, silicon carbide, titanium carbide, titaniumoxide and iron oxide.

According to another preferred embodiment of the present invention, amethod for manufacturing a wafer for magnetic heads includes the step ofpreparing a sintered body by sintering a mixture of a first type ofpowder particles and a second type of powder particles. In this case,when the first type of powder particles is made of a first material, thesecond type of powder particles is preferably made of a second materialthat has a different etch susceptibility from the first material. Themethod preferably further includes the step of writing ID information onthe surface of the sintered body by defining a first concave region to adepth of at least about 10 nm under the surface of the sintered body anda second concave region under the first concave region, respectively.The first concave region is preferably defined by etching away both thefirst and second types of powder particles, while the second concaveregion is preferably defined by selectively etching away only the firsttype of powder particles.

According to a further preferred embodiment of the present invention, asintered body is preferably obtained by sintering a mixture of a firsttype of powder particles and a second type of powder particles. When thefirst type of powder particles is made of a first material, the secondtype of powder particles is preferably made of a second material thathas different etch susceptibility from the first material. In thissintered body, a first concave region is preferably defined to a depthof at least about 10 nm under the surface of the sintered body and asecond concave region is preferably defined under the first concaveregion, respectively, thereby writing ID information on the surface ofthe sintered body. The first concave region is preferably defined byetching away both the first and second types of powder particles, whilethe second concave region is preferably defined by selectively etchingaway only the first type of powder particles.

In one preferred embodiment of the present invention, the second concaveregion preferably has a depth of at least about 50 nm as measured fromthe bottom of the first concave region.

In this particular preferred embodiment, the second concave regionpreferably has a depth of at most about 5 μm as measured from the bottomof the first concave region.

In another preferred embodiment, the first and second types of powderparticles may both have a mean particle size of about 0.3 μm to about5.0 μm.

In still another preferred embodiment, a variation ΔR in reflectance dueto an etching process is at least about 25% with respect to light havinga particular wavelength, the variation ΔR being determined by(R2−R1)/R2, where R1 is the reflectance of a portion of the surface ofthe sintered body that has been subjected to the etching process and R2is the reflectance of another portion of the surface of the sinteredbody that has not been subjected to the etching process.

In this particular preferred embodiment, the particular wavelength ispreferably included in the wavelength range of light to be radiatedtoward the sintered body to read the ID information optically.

In yet another preferred embodiment, a portion of the surface of thesintered body, which has not been subjected to the etching process,preferably has a surface roughness of at most about 5 nm.

In yet another preferred embodiment, the first and second materials arepreferably compounds selected from the group consisting of aluminumoxide, aluminum nitride, silicon oxide, silicon nitride, zirconiumoxide, zirconium nitride, silicon carbide, titanium carbide, titaniumoxide and iron oxide.

Yet another preferred embodiment of the present invention provides awafer for magnetic heads. The wafer preferably includes a sintered bodyand an insulating film provided on the sintered body. The sintered bodyis preferably obtained by sintering a mixture of a first type of powderparticles and a second type of powder particles. When the first type ofpowder particles is made of a first material, the second type of powderparticles is preferably made of a second material that has differentetch susceptibility from the first material. In the sintered body, afirst concave region is preferably defined to a depth of at least about10 nm under the surface of the sintered body and a second concave regionis preferably defined under the first concave region, respectively,thereby writing ID information on the surface of the sintered body. Thefirst concave region is preferably defined by etching away both thefirst and second types of powder particles, while the second concaveregion is preferably defined by selectively etching away only the firsttype of powder particles.

According to yet another preferred embodiment of the present invention,a magnetic head preferably includes a substrate and anelectrical/magnetic transducer provided on the substrate. The substrateis preferably made of a mixture of a first type of powder particles anda second type of powder particles. When the first type of powderparticles is made of a first material, the second type of powderparticles is preferably made of a second material that has a differentetch susceptibility from the first material. In the substrate, a firstconcave region is preferably defined to a depth of at least about 10 nmunder the surface of the substrate and a second concave region ispreferably defined under the first concave region, respectively, therebywriting ID information on the surface of the substrate. The firstconcave region is preferably defined by etching away both the first andsecond types of powder particles, while the second concave region ispreferably defined by selectively etching away only the first type ofpowder particles.

According to yet another preferred embodiment of the present invention,a storage medium drive preferably includes a magnetic head, whichincludes a substrate and an electrical/magnetic transducer provided onthe substrate, a storage medium with a magnetic recording film from/onwhich information is read or written by the magnetic head, and a motorto drive the storage medium. In the magnetic head, the substrate ispreferably made of a mixture of a first type of powder particles and asecond type of powder particles. When the first type of powder particlesis made of a first material, the second type of powder particles ispreferably made of a second material that has a different etchsusceptibility from the first material. In the substrate, a firstconcave region is preferably defined to a depth of at least about 10 nmunder the surface of the substrate and a second concave region ispreferably defined under the first concave region, respectively, therebywriting ID information on the surface of the substrate. The firstconcave region is preferably defined by etching away both the first andsecond types of powder particles, while the second concave region ispreferably defined by selectively etching away only the first type ofpowder particles.

Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a slider for a magnetic head.

FIG. 1B is a perspective view illustrating a bar yet to be divided intomultiple sliders for a magnetic head.

FIG. 1C is a perspective view illustrating a substantially rectangularsintered wafer.

FIG. 2 schematically illustrates a conventional laser marking process.

FIG. 3 is a cross-sectional view showing a deeply inscribed portionformed by a conventional laser marking process.

FIG. 4A is a cross-sectional view of an inscribed portion defined by aconventional marking process including a non-selective etching process.

FIG. 4B is a cross-sectional view of an inscribed portion defined by amarking process including a selective etching process.

FIG. 4C is a cross-sectional view of an inscribed portion defined by amarking process in which the selective etching process and thenon-selective etching process are carried out in this order.

FIG. 5 is a cross-sectional view schematically illustrating an inscribedportion according to a preferred embodiment of the present invention.

FIGS. 6A, 6B and 6C are cross-sectional views showing respective processsteps of the selective etching process to be performed for markingpurposes.

FIG. 6D is a plan view schematically illustrating the etched surface andnon-etched surface of a ceramic wafer.

FIG. 7 is a cross-sectional view of a hard disk drive according to apreferred embodiment of the present invention.

FIG. 8 is a graph showing a relationship between the variation ΔR inreflectance as a result of a selective etching process and the depth t2of a second concave region.

FIG. 9 is an AFM photograph showing the non-etched surface of a sinteredbody in a specific example of a preferred embodiment of the presentinvention.

FIG. 10 is an AFM photograph showing the etched surface of a sinteredbody in a specific example of a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First, it will be described with reference to FIGS. 4A through 4C howthe cross-sectional shape of a concave portion, formed by an etchingprocess, may change with the specific method of the etching process.

FIG. 4A illustrates a cross section of a concave portion defined by aconventional non-selective etching process. Specifically, FIG. 4Aillustrates a cross section of a sintered wafer 40, which is made up oftwo types of powder particles with mutually different etchsusceptibilities. In FIGS. 4A, 4B and 4C, the width of an etched portionon the surface of the sintered wafer 40 (i.e., the width of an inscribedgroove) is identified by C. The bottom 42 of the etched portion will bereferred to herein as an “etched surface”. The etched surface 42 of thewafer 40 is located below the non-etched surface 41 of the wafer 40 andthere are steep slopes between the non-etched surface 41 and the etchedsurface 42.

In the conventional non-selective etching (i.e., physical etching)process, even when the sintered wafer 40 is made up of two types ofpowder particles having mutually different etch susceptibilities, thosetwo types of powder particles are etched away at substantially equalrates. Thus, a concave portion with a substantially flat bottom 42 isdefined on the surface of the sintered wafer 40 as shown in FIG. 4A. Asa result of such a non-selective etching process, there will be nosubstantive difference between the reflectance of the flat surface(i.e., the non-etched surface) 41 of the sintered wafer 40 and that ofthe flat bottom (i.e., the etched surface) 42 of the concave portionthereof. In that case, even if the concave portion has a depth exceedingabout 10 μm, it is difficult to achieve a desired contrast that is highenough to make the ID information recognizable at a sufficiently highread rate.

Such a non-selective etching technique is often adopted in the prior artto define a deep concave portion efficiently enough (i.e., at asufficiently high etch rate). In other words, a deep concave portioncannot be defined at an increased etch rate unless the non-selectiveetching technique is adopted.

FIG. 4B shows a cross section of a concave portion defined by the methodthat was disclosed by the applicant of the present application inJapanese Laid-Open Publication No. 2001-334753. In the exampleillustrated in FIG. 4B, a selective etching process is carried out underconditions that allows the two types of powder particles of the sinteredwafer 50 to exhibit mutually different etch susceptibilities. As aresult, one of the two types of powder particles (i.e., the hatchedparticles) with the higher etch susceptibility is etched earlier andfaster than the other type of powder particles (i.e., the non-hatchedparticles) with the lower etch susceptibility As a result, an unevennessof very small size is defined on the etched surface 42. In thatunevenness, the width of the depressed portions is approximately equalto the size of the hatched particles and the depth thereof is changeablewith the amount of time in which the etching process is carried out.

In a ceramic sintered wafer, which is now used extensively for magneticheads, particles thereof typically have a mean particle size of about0.3 μm to about 5.0 μm, which is much smaller than the width C (e.g.,about 1 μm to about 20 μm) of the concave portion defined by the markingprocess. Thus, the bottom of the concave portion defined by the etchingprocess (i.e., the etched surface 42) diffuses or scatters the lightthat has been radiated from an ID information reader. That is to say,the reflectance of the etched surface 42 becomes lower than that of theflat surface (i.e., the non-etched surface) 41. In this manner, adifference is created between the reflectances of the etched andnon-etched surfaces 42 and 41 of the sintered wafer 50. As a result,even if the concave portion has a relatively shallow depth (or etchdepth), the reflected light still achieves a sufficiently high contrast.However, the reflectance of the surface of the sintered wafer alsodepends on the wavelength or the spectrum of the light radiated.Accordingly, a sufficient difference (which is preferably at least about25%) in reflectance needs to be produced for the light to be actuallyused by the optical ID information reader.

However, if the concave portion has a shallow depth as in the exampleillustrated in FIG. 4B, then the boundary between the etched andnon-etched portions (i.e., the border lines of a character or a numeralrepresenting the ID information) would be indefinite, thus possiblycausing read errors (or recognition errors). In particular, if theraised portions on the etched surface 42 have their height decreased asa result of a polishing process to be performed on the surface of thewafer after the wafer has been marked with the ID information, then thereflectance would decrease and those read errors would increase. Also,if the inscribed groove has a narrow width C, there will be a decreasednumber of depressed and raised portions on the bottom of the groove. Inthat case, the reflectance itself drops and the read errors may furtherincrease.

To overcome these problems, according to a preferred embodiment of thepresent invention, first, a “selective etching process” is carried outto selectively etch away one of two types of powder particles withmutually different etch susceptibilities at a higher rate, and then a“non-selective etching process” is carried out to etch away both ofthose two types of powder particles at almost equal rates. In thismanner, a first concave region is defined on the surface of a sinteredbody by etching away both of the two types of powder particles and asecond concave region is defined under the first concave region byselectively etching away one of the two types of powder particles.

FIG. 4C illustrates a cross section of an inscribed groove defined bysuch a two-step etching process. As shown in FIG. 4C, this inscribedgroove has a cross-sectional shape to be obtained by combining theinscribed groove shown in FIG. 4A with the inscribed groove shown inFIG. 4B so to speak. This cross-sectional structure will be described infurther detail with reference to FIG. 5. FIG. 5 is a cross-sectionalview schematically illustrating the profile of the inscribed grooveshown in FIG. 4C. In FIG. 5, the first concave region, defined byetching away both of the two types of powder particles alike, isidentified by the reference numeral 60 a while the second concaveregion, defined by etching away just one of the two types of powderparticles selectively, is identified by the reference numeral 60 b.

For example, in an AlTiC wafer made of a mixture of Al₂O₃ particles andTiC particles, the process step of selectively etching away the TiCparticles and the process step of etching away both of the Al₂O₃ and TiCparticles at almost equal rates may be carried out back to back, therebydefining a structure such as that shown in FIG. 5. In that case, thedepth t1 of the first concave region 60 a is the etch depth of thenon-selective etching process (i.e., the etch rate of the non-selectiveetching process×time) while the depth t2 of the second concave region 60b is the etch depth of the selective etching process (i.e., the etchrate of the selective etching process×time). In this example, the TiCparticles are etched in both of the selective and non-selective etchingprocesses. Accordingly, in the overall etching process, the etch rate ofthe TiC particles is defined by dividing the total depth of theinscribed groove (i.e., t1+t2) by the total etch time. It should benoted that the shape shown in FIG. 5 may also be obtained even byperforming the non-selective etching process first and then theselective etching process.

The depth t1 of the first concave region 60 a is measured with respectto the non-etched surface of the wafer, while the depth t2 of the secondconcave region 60 b is measured with respect to the bottom of the firstconcave region 60 a. These depths may be measured with an atomic forcemicroscope (AFM).

The present inventors discovered and confirmed via experiments that thereflectance of the etched surface changed with the depth t2 of thesecond concave region 60 b but did not depend on the depth t1 of thefirst concave region 60 a. On the other hand, the depth of field of theoptical character recognition does change with the depth t1 of the firstconcave region 60 a. In a preferred embodiment of the present invention,the first concave region 60 a preferably has a depth t1 of about 10 nmor more to increase the recognition rate. To further increase therecognition rate, the first concave region 60 a preferably has a deptht1 of at least about 20 nm, more preferably at least about 25 nm. Theupper limit of the depth t1 is not particularly limited because thefirst concave region 60 a sometimes has a depth t1 that does not makethe character unrecognizable even when the back surface of the wafer isprocessed by a subsequent process step. However, the deeper the firstconcave region 60 a (i.e., the greater the depth t1), the longer thetime it takes to finish the non-selective etching process. Thus, thefirst concave region 60 a preferably has a depth t1 of at most about 5μm.

The present inventors also discovered via experiments that when such anAlTiC wafer was used, a difference in reflectance of at least about 25%could be obtained by setting the depth t2 of the second concave region60 b at about 50 nm or more, and that the difference in reflectanceincreased with the depth t2. Specifically, the results of theexperiments revealed that the second concave region 60 b preferably hasa depth t2 of at least about 100 nm, more preferably at least about 150nm. The upper limit of the depth t2 of the second concave region 60 b isnot particularly limited, either. However, considering the time it takesto finish the selective etching process, the depth t2 may be at mostabout 5 μm, for example.

Hereinafter, specific preferred embodiments of the present inventionwill be described with reference to the accompanying drawings.

Method of Marking Sintered Body

First, a sintered wafer is prepared by a known method.

In a preferred embodiment of the present invention, the sintered waferto be marked with ID information is obtained by mixing two types ofpowder particles that should be etched at mutually different rates undera particular combination of etching conditions. A ceramic made up of atleast two compounds selected from the group consisting of aluminumoxide, aluminum nitride, silicon oxide, silicon nitride, zirconiumoxide, zirconium nitride, silicon carbide, titanium carbide, titaniumoxide and iron oxide can be used effectively as such a material for thesintered wafer.

One of the important features of preferred embodiments of the presentinvention is that the powder particles for use to make the sinteredwafer exhibit at least two different etch susceptibilities. For example,even when two compounds have the same composition that is commonlyrepresented by the identical chemical formula Al₂O₃, those two compoundsmay exhibit significantly different etch susceptibilities depending onwhether or not impurities such as rare earth oxides or alkaline earthoxides are added thereto and also depending on the specificconcentrations of the impurities. Stated otherwise, it is also possibleto intentionally impart mutually different etch susceptibilities tofirst and second powders that have the same basic composition of Al₂O₃.Thus, a marking method according to a preferred embodiment of thepresent invention can also be carried out on a sintered wafer that ismade up of at least two types of Al₂O₃ powders with mutually differentetch susceptibilities.

Hereinafter, a specific example of a preferred embodiment of the presentinvention will be described with reference to FIGS. 6A through 6D. Inthe example illustrated in FIGS. 6A through 6D, the sintered wafer 60 isa composite wafer made of an Al₂O₃—TiC ceramic, i.e., consisting of twotypes of materials of Al₂O₃ and TiC.

First, as shown in FIG. 6A, before the sintered wafer 60 is subjected toan etching process for marking purposes, the surface of the sinteredwafer 60 is masked except for its portions to be etched away.Specifically, the surface of the sintered wafer 60 is covered with amasking layer 51 with sufficient etch resistivity. When the maskinglayer 51 is made of a positive photoresist, for example, the positivephotoresist may be applied to a thickness of about 1 μm to about 2 μm onthe surface of the sintered wafer 60 with a spinner, for example, andthen baked. As such a photoresist material, OFPR-800 produced by TokyoOhka Kogyo may be used, for example.

Next, after the photoresist has been baked, the photoresist is exposedto a g-line ray at an intensity of about 200 mJ/cm² by way of aphotomask or a “Titler” marker that defines an ID information pattern.This process step will be referred to herein as an “exposure processstep”.

When the exposure process step is finished, a development process stepis carried out, thereby obtaining a resist mask 51, having an opening(with a width C) that defines a pattern corresponding to the IDinformation pattern, on the sintered wafer 60.

Subsequently, the sintered wafer 60 covered with the resist mask 51 isloaded into an etching process chamber (not shown) of a reactive ionetching (RIE) system, thereby subjecting the wafer 60 to a predeterminedetching process. The etching gases for use in this etching process maybe appropriately selected according to the specific material to beetched. In this preferred embodiment, the Al₂O₃—TiC ceramic wafer isused as described above. Thus, CF₄ gas or SF₆ gas is preferably used,for example. When CF₄ gas is used, the electrical discharge of the CF₄gas generates radical species and ions. In the reaction chamber of theRIE system, the following chemical reactions are produced:

Fundamental Reaction Process:

 CF₄→CF₃+F

Inverse Reaction Process:CF₃+F→CF₄2F→F₂2CF₃→C₂F₆CF₃+F₂→CF₄+F

As a result of these reactions, CF₃ and F are generated as radicalspecies. An etching process to which F contributes has a selectivity soas to etch TiC earlier and faster than Al₂O₃. In this preferredembodiment, the selective etching process is preferably carried outunder such conditions that the etch rate of TiC becomes several times ashigh as the etch rate of Al₂O₃.

On the other hand, a physical etching process, to which ions generatedby the electrical discharge contribute, has no such selectivity, thusetching Al₂O₃ and TiC at almost equal rates. It should be noted that theetch rate of Al₂O₃ may be slightly higher than that of TiC depending onthe conditions.

In this manner, in the RIE system, the ion-induced physical etchingaction competes with the radical-species-induced chemical etchingaction. Thus, by controlling the gas pressure and the voltage applied tothe electrode, the RIE system can readily switch the selective etchingprocess and the non-selective etching process. Specifically, when thegas pressure is set relatively high and the voltage relatively low, theradical species density exceeds the ion density, thus accelerating theselective etching process. Conversely, when the gas pressure is setrelatively low and the voltage relatively high, the ion density exceedsthe radical species density, thus accelerating the non-selective etchingprocess.

As used herein, the “selective etching process” means an etching processin which the etch rate A of one type of material (i.e., particles) to bechemically etched relatively quickly relative to the etch rate B of theother type of material (i.e., particles) to be chemically etchedrelatively slowly is at least about 3. That is to say, the selectiveetching process satisfies 3≦A/B. On the other hand, the “non-selectiveetching process” is carried out under such conditions as to satisfy0.7≦A/B≦1.3. Accordingly, an intermediate etching process that satisfies1.3<A/B<3 is neither selective nor non-selective.

If the gas pressure and the pressure inside the RIE system are definedat intermediate values, then the etching action produced will be halfwaybetween the selective etching action and the non-selective etchingaction. A cross-sectional structure such as that shown in FIG. 5 mayalso be formed even by such an intermediate etching process. However,the electrical discharge producing such an etching action is toounstable to control the etch rate as intended. Also, such an unstableetching action likely causes the etch residue problem (to be describedlater). For these reasons, the intermediate etching process, satisfying1.3<A/B<3, is not preferred.

Thus, in this preferred embodiment of the present invention, theselective and non-selective etching processes are sequentially carriedout by switching the etching conditions appropriately such that thecross-sectional structure shown in FIG. 5 is formed constantly.

It should be noted that the selective etching process does not have toperformed just once but may be repeated a number of times. The samestatement is true of the non-selective etching process. Also, theselective and non-selective etching processes may be carried in anarbitrary order. Nevertheless, the non-selective etching process ispreferably carried out as the last etching process. This is because theetch residue to be left on the wafer by the selective etching process inmany cases is preferably decomposed and cleaned off the wafer by theion-induced non-selective etching process.

When the etching process is finished, the exposed portion of thesintered wafer 60 (i.e., the etched surface 42), which is not coveredwith the resist mask 51, has unevenness of a very small size on thebottom of the concave portion that is deeper than the non-etched surfaceas shown in FIG. 6B.

Next, as shown in FIG. 6C, the resist mask 51 is removed from thesintered wafer 60. The etched surface 42 with the unevenness of the verysmall size has a reflectance R1, which is lower than the reflectance R2of the relatively flat non-etched surface 41 (i.e., R1<R2). FIG. 6D is aplan view schematically illustrating the unevenness of the etchedsurface 42.

The layout of the etched surface is defined by the planar pattern of theresist mask 51. The planar pattern of the resist mask 51, in turn, isarbitrarily defined by a photomask or a “Titler” marker for use in anexposure process. Thus, any desired ID information such as characters,signs or barcodes may be written on the sintered wafer 60.

To decrease the reflectance R1 of the etched surface 42, the line widthof the characters, signs or barcodes is preferably sufficiently greaterthan the mean particle size of the particles that make up the sinteredwafer 60.

On the other hand, to increase the reflectance R2 of the non-etchedsurface 41, the non-etched surface 42 preferably has a decreased surfaceroughness so as to be planarized. For that purpose, it is effective topolish the surface of the sintered wafer 60 before subjecting the wafer60 to the etching process described above.

The greater the variation ΔR=((R2−R1)/R2) in reflectance due to theetching process, the higher the contrast achieved by the light that hasbeen radiated toward the surface of the sintered wafer 60. In theexample illustrated in FIG. 6D, the etched surface 42 looks darker thanthe other portions, thereby making the ID information such as inscribedletters recognizable accurately.

According to the preferred embodiment of the present invention describedabove, a structure such as that shown in FIG. 5 is defined to increasenot only the contrast by utilizing the fine unevenness on the bottom ofa groove with an appropriate depth but also the profile of the inscribedgroove. As a result, the ID information can be recognized at anincreased rate.

Method for Manufacturing Magnetic Head Wafer

Hereinafter, a preferred embodiment of a method for manufacturing awafer for magnetic heads according to the present invention will bedescribed.

First, an Al₂O₃—TiC based ceramic wafer, for example, is prepared. Onthe back surface of such a composite wafer (i.e., opposite to the frontsurface thereof on which magnetic thin films are stacked), IDinformation is marked by the marking process described above.

Thereafter, an amorphous aluminum oxide film is deposited to a thicknessof about 0.5 μm to about 20 μm on the front surface of the wafer by asputtering process, for example. Subsequently, the surface of theamorphous aluminum oxide film is planarized to complete the preparatorystage of the process for manufacturing a thin-film magnetic head wafer.

Then, various magnetic thin films are stacked on this thin-film magnetichead wafer. When the wafer obtained in this manner is divided intomultiple bars 20 as shown in FIG. 1C, a number of identifiers 13 will bemarked on each of those bars 20 as shown in FIG. 1B. Thereafter, each ofthose bars 20 is further divided into a number of magnetic heads, oneach of which its own identifier 13 will be written as shown in FIG. 1A.In this manner, the respective magnetic heads are easily identifiable bytheir serial numbers. Thus, the magnetic head manufacturing process canbe controlled as in the prior art.

The preferred embodiment of the present invention described aboveprovides a method for manufacturing a magnetic head that can solve thecontamination problem, normally caused by the laser marking process, andthat can be effectively used for a sufficiently long time even in astorage medium drive that should be free from dust as completely aspossible. As a result, not only the production yield of magnetic headsbut also the reliability of magnetic recording/reproducing apparatusincluding such a magnetic head can be increased.

It should be noted that any arbitrary portion of the magnetic head maybe marked with the ID information That is to say, the present inventionis in no way limited to the specific marking locations shown in FIG. 1B.

Storage Medium Drive

FIG. 7 shows the cross-sectional structure of a storage medium drive(i.e., a hard disk drive) 70 including magnetic heads on which IDinformation is inscribed by the marking method according to thepreferred embodiment of the present invention described above. As shownin FIG. 7, the hard disk drive 70 preferably includes three magneticdisks 72, each including a magnetic recording layer (not shown), mediaspacers 74 provided between the magnetic disks 72, an electric motor 76for rotating the magnetic disks 72, and magnetic heads 78 for use toread and write information from/onto the magnetic disks 72 when broughtclose to the disks 72. The magnetic heads 78 are made by the methoddescribed above and each have inscribed ID information thereon. Each ofthese magnetic heads 78 is fixed to the end of its associated supportingmember 79 and can gain access to any arbitrary track on its associatedmagnetic disk 72 rotating. Information can be read out from, or writtenon, the magnetic recording layer (not shown) of the magnetic disk 72 byan electrical/magnetic transducer (not shown) provided for the magnetichead 78. The electric motor 76 is secured to the chassis 80 of the harddisk drive 70. A rotating cylinder 84 is fitted with the rotating shaft82 of the electric motor 76. The magnetic disks 72 rotate with therotating cylinder 84.

EXAMPLES

Hereinafter, a specific example of a preferred embodiment of the presentinvention will be described. In this example, an Al₂O₃—TiC based ceramicwafer, made of a compound sintered body including about 66 wt % of Al₂O₃and about 34 wt % of TiC, was used. This wafer was obtained by amachining process as a substantially rectangular (of about 50 mm square)thin wafer with a thickness of about 1.2 mm. Also, the surface of thewafer was finished by a mirror polishing process using diamond slurry(with a mean particle size of about 1 μm) so as to have a surfaceroughness Ra of about 0.5 nm to about 1.5 nm.

In this example, the back surface of the wafer was subjected to etchingprocesses under various conditions, thereby marking ID informationthereon. The marking process was carried out so as to inscribe a 7-digitsymbol consisting of characters or numerals on each head portion of thewafer. The identifier does not have to be such a symbol but may also bea two-dimensional barcode. Approximately 3,000 identifiers (inapproximately 21,000 characters) were inscribed on the back surface of asingle wafer. The sizes of each of those symbols inscribed were about100 μm by about 150 μm. The detailed conditions for the etchingprocesses that were carried out for marking purposes are shown in thefollowing Table 1:

TABLE 1 Sample System Etching conditions 1 ICP-RIE A × 0 min. + B × 4min. 2 ICP-RIE A × 2 min. + B × 4 min. 3 ICP-RIE A × 5 min. + B × 4 min.4 ICP-RIE A × 0 min. + B × 2 min. 5 ICP-RIE A × 2 min. + B × 2 min. 6ICP-RIE A × 5 min. + B × 2 min. 7 Cnv. RIE C × 0 min. + D × 12 min. 8Cnv. RIE C × 4 min. + D × l2 min. 9 Cnv. RIE C × 7.5 min. + D × 12 min.

In the “system” column of Table 1, “ICP-RIE” stands for an inductivelycoupled plasma reactive ion etching system, which is a parallel plateplasma enhanced etching system including magnetic field generating coil.On the other hand, “Cnv. RIE” stands for a conventional reactive ionetching system, which is a parallel plate plasma enhanced etching systemof the type applying no magnetic fields. In each of these etchingsystems, an RF power supply is connected to the electrode on a waferholder and plasma of the etching gas is generated between the upper andlower electrodes. The ICP-RIE normally achieves a higher etch rate thanthe Cnv. RIE because the electron density in the plasma can be higher inthe ICP-RIE system than in the Cnv. RIE system. However, if a selectiveetching process is simply carried out by using the ICP-RIE system, theetch rate of Al₂O₃ decreases significantly.

Also, in the “etching conditions” column of Table 1, the referenceletters A, B, C and D denote the four sets of etching conditions shownin the following Table 2. For example, “A×2 min.+B×4 min.” means thatthe etching process should be performed for about 2 minutes under theconditions A and for about 4 minutes under the conditions B. It shouldbe noted that only the selective etching process was performed on thesamples Nos. 1, 4 and 7, which represent comparative examples for thepresent invention.

TABLE 2 Power Pressure of Al₂O₃ TiC rate Condi- density CF₄ gas rate(nm/ tions System (W/cm²) (10 × 10⁻³ Torr) (nm/min.) min.) A ICP-RIE1.75 4.0 30 30 B ICP-RIE 0.8 2.0 5 25 C Cnv. RIE 0.9 9.0 20 20 D Cnv.RIE 0.18 20.0 0.5 10

In Table 2, the power density is the density of the power, supplied tothe etching system, as measured per unit electrode area. In thisexample, CF₄ gas was used as an etching gas. Also, in Table 2, the“Al₂O₃ rate” denotes the etch rate of the Al₂O₃ particles while the “TiCrate” denotes the etch rate of the TiC particles.

As can be seen from Table 2, according to the two sets of conditions Aand C, the etch rate of Al₂O₃ was approximately equal to that of TiC,thus realizing a non-selective etching process. Thus, under each ofthese two sets of etching conditions, the ion-induced physical etchingaction was dominating. On the other hand, according to the other twosets of conditions B and D, the etch rate of TiC was much higher thanthat of Al₂O₃, thus realizing a selective etching action in such amanner as to etch TiC faster and earlier than Al₂O₃. Accordingly, undereach of these two sets of conditions, the radical-species-inducedchemical etching action was dominating.

As shown in Table 1, each of the samples Nos. 1, 2 and 3 was subjectedto the selective etching process under the conditions B forapproximately 4 minutes. However, these samples Nos. 1, 2 and 3 weresubjected to the non-selective etching process under the conditions Afor 0, 2 and 5 minutes, respectively. On the other hand, each of thesamples Nos. 4, 5 and 6 was subjected to the selective etching processunder the conditions B for approximately 2 minutes. However, thesesamples Nos. 4, 5 and 6 were subjected to the non-selective etchingprocess under the conditions A for 0, 2 and 5 minutes, respectively.That is to say, the selective etching process under the conditions B wascarried out on the two groups of samples Nos. 1, 2 and 3 and Nos. 4, 5and 6 for mutually different amounts of time.

As for samples Nos. 1 to 9, on which the ID information was inscribedunder the various conditions shown in Table 2, the depths t1 and t2 ofthe first and second concave regions defined, the variation ΔR inreflectance, and the readability were estimated. The results are shownin the following Table 3:

TABLE 3 Depth t1 (nm) Depth t2 (nm) Variation of first of second ΔR (%)in Readability Sample Concave region concave region reflectance (%) 1 590 62.0 95.5 2 80 90 62.6 99.5 3 155 90 62.0 99.5 4 5 45 23.1 0 5 80 4523.9 0 6 155 45 24.5 12.5 7 5 120 63.4 96.5 8 80 120 61.6 99.5 9 155 12064.0 99.5

In Table 3, the variation ΔR in reflectance (which is given by(R2−R1)/R2 ) was obtained with respect to light having a wavelength ofabout 546 nm. The greater this variation ΔR in reflectance, the greaterthe difference between the reflectance R2 of the non-etched surface andthe reflectance R1 of the etched surface would be. The readability wasmeasured with a reader that used the light having a wavelength of about546 nm as its illumination. Alternatively, white light or any othervisible radiation may also be used as the illumination. Also, acuReaderproduced by Komatsu Ltd. may be used as the reader.

As can be seen from the results shown in Table 3, the non-selectiveetching process was not carried out on the samples Nos. 1, 4 and 7representing comparative examples. Thus, in the samples Nos. 1, 4 and 7,the first concave region had a depth t1 of about 5 nm, which is muchsmaller than 20 nm, and substantially no first concave region wasdefined. It should be noted that even when the first concave region hasa depth t1 of less than about 20 nm, a variation in reflectance as highas more than 60% can be obtained as in the sample No. 1 by performingthe selective etching process sufficiently. However, even if thevariation in reflectance exceeds 60% but if the first concave region hasa depth t1 of only 5 nm, the resultant readability is just about 95.5%as in the sample No. 1.

The present inventors discovered and confirmed via experiments that toachieve a readability as high as about 97% or more, the first concaveregion needs to have a depth t1 of at least about 10 nm. Meanwhile, evenif the first concave region defined has a depth t1 of about 80 nm ormore but if the selective etching process is carried out insufficiently,the variation in reflectance is less than about 35% and the readabilitywas zero or at most quite low as in the samples Nos. 4, 5 and 6.

In view of these considerations, to make the ID information inscribedaccurately readable, a variation ΔR in reflectance of at least about 25%should be achieved by providing the second concave region, and thenon-selective etching process should be carried out such that the firstconcave region has a depth of at least about 10 nm.

FIG. 8 is a graph showing a relationship between the variation ΔR inreflectance as a result of the selective etching process and the deptht2 of the second concave region. In FIG. 8, the ordinate represents thevariation ΔR in reflectance, while the abscissa represents the depth t2of the second concave region, which increases leftward. The IDinformation inscribed is readable when the variation ΔR in reflectanceis at least about 25%.

FIG. 9 is an AFM photograph of the non-etched surface of a wafer, whileFIG. 10 is an AFM photograph of the etched surface of the wafer.

A marking method according to any of various preferred embodiments ofthe present invention described above achieves a reflected lightcontrast that is high enough to make the ID information inscribedaccurately recognizable. In addition, the concave portion defining theID information can have a sharpened profile, thus further increasing thereadability (i.e., the recognition rate) of the ID information. Inparticular, even after the wafer has been subjected to a polishingprocess, the unwanted decrease in readability is avoidable.

Also, according to preferred embodiments of the present invention, amagnetic head completed as a product generates a much smaller amount ofdust, thus increasing the reliability of a storage medium drive.

While the present invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

1. A method of marking a sintered body, comprising the steps of:preparing the sintered body by sintering a mixture of a first type ofpowder particles and a second type of powder particles, the first typeof powder particles being made of a first material, the second type ofpowder particles being made of a second material that has a differentetch susceptibility from the first material; and writing identificationinformation on the surface of the sintered body by forming a firstconcave region to a depth of at least about 10 nm under the surface ofthe sintered body and a second concave region under the first concaveregion, respectively, the first concave region being formed by etchingaway both the first and second types of powder particles, the secondconcave region being formed by selectively etching away only the firsttype of powder particles.
 2. The method of claim 1, wherein the step ofwriting the identification information includes the step of forming thesecond concave region to a depth of at least about 50 nm under thebottom of the first concave region.
 3. The method of claim 1, whereinthe step of writing the identification information includes the stepsof: performing a selective etching process such that the first type ofpowder particles are etched at a higher rate than the second type ofpowder particles; and performing a non-selective etching process suchthat the first and second types of powder particles are etched atsubstantially equal rates after the selective etching process has beenperformed.
 4. The method of claim 3, wherein the step of writing theidentification information includes the step of performing at least oneof the selective etching process and the non-selective etching processmultiple times.
 5. The method of claim 3, wherein the step of writingthe identification information includes the step of performing thenon-selective etching process at least as the last etching processthereof.
 6. The method of claim 3, wherein the selective etching processand the non-selective etching process are carried out by the sameetching system with etching conditions being changed.
 7. The method ofclaim 1, wherein the first and second types of powder particles bothhave a mean particle size of about 0.3 μm to about 5.0 μm.
 8. The methodof claim 1, wherein the first concave region has a line width of about 1μm to about 20 μm.
 9. The method of claim 3, wherein a variation ΔR inreflectance due to the selective etching process is at least about 25%with respect to light having a particular wavelength, the variation ΔRbeing determined by (R2 −R1 )/R2, where R1 is the reflectance of aportion of the surface of the sintered body that has been subjected tothe selective etching process and R2 is the reflectance of anotherportion of the surface of the sintered body that has not been subjectedto the selective etching process.
 10. The method of claim 9, wherein theparticular wavelength is included in the wavelength range of light to beradiated toward the sintered body to read the identification informationoptically.
 11. The method of claim 1, wherein a portion of the surfaceof the sintered body, which has not been subjected to the selectiveetching process, has a surface roughness of at most about 5 nm.
 12. Themethod of claim 1, wherein the depth of the second concave region isabout 50 nm to about 5 μm as measured from the bottom of the firstconcave region.
 13. The method of claim 1, wherein the first and secondmaterials are compounds selected from the group consisting of aluminumoxide, aluminum nitride, silicon oxide, silicon nitride, zirconiumoxide, zirconium nitride, silicon carbide, titanium carbide, titaniumoxide and iron oxide.
 14. A method for manufacturing a wafer formagnetic heads, comprising the steps of: preparing a sintered body bysintering a mixture of a first type of powder particles and a secondtype of powder particles, the first type of powder particles being madeof a first material, the second type of powder particles being made of asecond material that has a different etch susceptibility from the firstmaterial; and writing identification information on the surface of thesintered body by forming a first concave region to a depth of at leastabout 10 nm under the surface of the sintered body and a second concaveregion under the first concave region, respectively, the first concaveregion being formed by etching away both the first and second types ofpowder particles, the second concave region being formed by selectivelyetching away only the first type of powder particles.